1. Field of the Invention
This invention relates generally to a heat exchanger for transferring heat to an air stream from a heat source flowing in tubes, and, in particular, to a heater core in the passenger compartment of an automotive vehicle.
2. Description of the Prior Art
Conventionally, the tubes, which carry engine coolant through the heater core of an automotive vehicle, are arranged parallel to the stream of air that passes through the heater core. The heater core usually includes one or two rows of tubes, the second row being in-line and parallel to the first row.
It has long been understood that the heat transfer rate is much larger for turbulent flow than for laminar flow. Increasing turbulence of the air stream through the heater core is beneficial to the convection heat transfer rate and improves the overall performance of the heat exchanger. It is also more effective to increase the heat transfer on the air-side to improve the heat exchanger, as this is the more restrictive side compared to the rate of heat transferred from the fluid flowing inside the tube.
Generally, fins located between the tubes are secured to the outer surface of the tubes to enhance heat transfer from the coolant to the air stream. In order to induce turbulence in the air stream, fins on the outer surface of the tubes are usually mutually staggered and offset, but the tubes are aligned parallel to the air stream.
A need exists in the industry for techniques that improve heat transfer in a heater core without increasing its package size.